1. Field of the Invention
The present invention relates to a lamp device employing an electric-discharge lamp particularly adapted for mounting on automotive vehicles, and more specifically to a projector type automotive headlamp device which is capable of preventing undesirable electromagnetic waves generated by an electric-discharge lamp employed therein from being discharged outside the headlamp.
2. Description of the Prior Art
Recently, there have been proposed and developed various projector type automotive lamp devices having an electric-discharge bulb, such as a projector type headlamp, a projector type fog lamp, and the like, having superior light-distribution characteristics, which are applicable in high-grade automotive vehicles. One such projector type automotive headlamp has been disclosed in a SERVICE MANUAL Vol. 538 issued by Nissan Motor Co., Ltd. on August, 1987.
Such a conventional projector type headlamp assembly traditionally includes a metal lamp housing having a front opening for passing a light beam and an outer lens having a series of modified prisms or ridges that bend the light rays into a desired pattern. The outer lens is provided in the front end of the lamp housing to hermetically cover the front opening. The projector type headlamp assembly includes a lamp sub-assembly which is disposed in the lamp housing and constructed by a paraboloidal reflector and an electric discharge lamp located at the focal point of the reflector. The projector type headlamp assembly also includes an inner lens serving as a converging lens for converging and emitting light beams reflected from the reflector and those transmitted directly form the discharge lamp. The converted light beams are projected through the outer lens in the forward direction of the vehicle. An inner finisher or inner panel is disposed between the outer periphery of the inner converging lens and an outer peripheral section other than the front lens section of the outer lens, for preventing light beams created by the discharge lamp from transmitting through an undesirable region other than the front lens section of the outer lens and for serving as a blind member obstructing a visual field to the interior of the housing. A shade member is also provided between the inner converging lens and the lamp sub-assembly, for defining and projecting a predetermined shadow in the forward direction of the vehicle in conjunction with the inner converging lens, thereby preventing undesirable leakage of light beams above the required headlight emitting level. As set forth above, in the prior art projector type headlamp devices, the combination of the inner converging lens and the shade member provides superior light-distribution characteristics for a dim, or low beam headlight.
Furthermore, Japanese Patent First Publication (Tokkai) Showa 61-259401 discloses a two-filament type headlamp including an electric-discharge bulb and a front lens being comprised of a plurality of lens segments respectively having different transmittance.
However, in the previously described conventional lamp devices employing an electric-discharge bulb, there is a problem that undesirable electromagnetic waves generated by the electric-discharge lamp (bulb) pass through the outer lens and are discharged outside of the lamp housing. As is generally known, such electromagnetic waves are harmful to various electronic parts, for example a large-scale integration (LSI) device employed in the vehicle so as to provide various control operations, and further causes generation of electromagnetic noise.